1. Field of the invention
The present invention relates to a front wheel-and rear-wheel drive vehicle in which one of either front road wheels or rear road wheels is driven by means of a motor such as an engine and the other is driven by means of another motor such as an electric motor.
2. Description of the Related Art
A Japanese Patent Application First Publication No. Heisei 8-300965 published on Nov. 19, 1996 (which corresponds to a U.S. Pat. No. 5,788,005 issued on Aug. 4, 1998) exemplifies a previously proposed front wheel-and rear-wheel drive vehicle in which the vehicle can run utilizing both of a mechanical energy caused by an internal combustion engine and an electrical energy caused by an electric motor.
In the front wheel-and rear-wheel drive vehicle disclosed in the above-described United States Patent, when front left and right road wheels are driven by means of the engine and rear left and right road wheels are driven by means of the electric motor, a driving force applied to the front road wheels and a slip rate of the front road wheels are detected. On the basis of a correlation between these detected values, a frictional coefficient xcexc on a road surface is detected.
When the previously proposed front wheel-and rear-wheel drive vehicle is started, the motor is operated. at an initial stage of the vehicle start if the frictional coefficient xcexc detected before the vehicle has stopped is equal to or below a predetermined value xcexcs. Hence, the rear road wheels are driven by means of the motor when the vehicle is started on the road surface having the low frictional coefficient to perform a start assistance through the rear road wheels.
However, the frictional coefficient xcexc of the road surface is detected through the correlation between the driving force exerted on the front road wheels and the slip rate of the same road wheels and the drive of the motor to drive the rear road wheels is controlled on the basis of the road frictional coefficient xcexc on the front road wheels. Hence, for example, if the frictional coefficient xcexc is different between positions at the front and rear road wheels, the rear road wheels are controlled on the basis of the frictional coefficient of the road surface which is different from an actual frictional coefficient on the motor driven rear road wheels.
Consequently, an appropriate drive control of the rear road wheels cannot be achieved such as due to an occurrence of the slip.
It is therefore an object of the present invention to provide a front wheel-and rear-wheel drive vehicle which can appropriately control the drive of the motor in accordance with a road surface situation on which the vehicle is running.
The above-described object can be achieved by providing a front wheel-and rear-wheel drive vehicle comprising: a motor to develop a mechanical energy and to drive either one of front road wheels or rear road wheels of the vehicle; another motor to develop the mechanical energy and to drive the other of the front road wheels or the rear road wheels; a drive controller to control a driving force of the other motor; a front-and-rear road wheel velocity difference detector to detect a front-and-rear road wheel velocity difference between the front and rear road wheels; a driver""s vehicular acceleration intention detector to detect a manipulated variable representing a driver""s acceleration intention; a target torque calculating section that calculates a target torque outputted from the other motor in accordance with the detected front-and-rear road wheel velocity difference and manipulated variable representing the driver""s acceleration intention; another motor driven wheel acceleration detector to detect an acceleration of another motor driven road wheel driven by means of the other motor; and a target torque corrector to correct the target torque on the basis of the acceleration of the other motor driven road wheel detected by the other motor driven wheel acceleration detector and the manipulated variable representing the driver""s vehicular acceleration intention detected by the driver""s vehicular acceleration intention detector.